This invention relates to the art of making heat-treated polybenzoxazole fibers.
It is known to spin and heat-treat fibers that contain polybenzazole polymer. See, e.g., Wolfe, U.S. Pat. No. 4,533,693 (Aug. 5, 1985) at col. 166-174; Takeda, Japanese Kokai 2(1990)-84511 (published Mar. 26, 1990); and Ledbetter et al., "An Integrated Laboratory Process for Preparing Rigid Rod Fibers from the Monomers," The Materials Science and Engineering of Rigid Rod Polymers at 253, 259-61 (Materials Research Society 1989), which are incorporated herein by reference. Ordinarily, a dope is formed containing the polymer and a solvent acid. The dope is forced through a spinneret and drawn across an air gap. It is contacted with a coagulating liquid, usually water, to coagulate the polymer and form a fiber. The fiber is washed to remove residual acid. The resulting fiber is heat-treated to improve its modulus.
Within those broad process steps there is still significant room for improvement. The most desirable process conditions may vary from fiber-to-fiber. What is needed is a process specifically adapted for making the best polybenzoxazole fibers.